The present invention relates to a male fastening tool to be used to fasten a member to a portion where a sealing property is demanded.
Various members are fixed to portions respectively where they are to be fastened by using a fastening tool such as a bolt, a nut, a plug, and the like. In dependence on a portion, it is necessary to fasten a member with preferable sealing performance against leak of water and oil.
To fasten the member to the portion where preferable sealing performance is demanded, a sealing ring such as a rubber ring is used in combination with a metal washer ring at the portion where the preferable sealing performance is demanded. But the use of such rings may thicken the portion to which the member should be fastened with preferable sealing performance and may cause defective sealing to occur owing to deviation of the sealing ring.
To overcome this problem, many fastening tools (for example, bolt) having sealing performance have been proposed. In the bolt disclosed in JPB1990-50328 2-50328, patent document 1), the annular groove part having the approximately semicircular cross section is concavely formed on the peripheral surface of the neck part disposed on the lower surface of the bolt head. There is provided the packing material having the integrally formed annular tongue edge part having the approximately triangular cross section. The annular tongue edge part can be filled in the filling part formed from the lower surface of the annular packing member fitted in the annular groove part to the open edge of the bolt hole. A member is fixed to the bolt hole by means of the annular groove part in cooperation with the packing member. Inside the annular groove part, there is provided the neck part-sealing part having the annular projected convexity projected inward or the annular concavity concaved outward.
The present applicant proposed the bolt as disclosed in WO2008/10523 (patent document 2). The bolt 1 of the patent document 2 has the bolt body 2 including the screw part 5, the head part 6 formed at the upper end of the screw part 5, and the flange part 7 formed at the lower end of the head part 6; and the unconductive resinous ring-shaped member 3 covering the peripheral portion of the flange part 7. The flange part 7 has the disk-shaped flange body portion 71 and the seat surface-forming portion 72 having the seat surface 73 which is extended toward the screw part from the lower surface of the flange body portion 71, has a smaller diameter than that of the flange body portion 71, and is pressed against the portion where the bolt is to be mounted. The resinous ring-shaped member 3 has the edge part 31 which is located at the position nearer to the lower end of the screw part 5 than the seat surface 73 and outward from the flange body portion 7 and the annular skirt part 32 whose diameter gradually increases to the edge part 31. The annular skirt part 32 deforms when the bolt is mounted on the portion where the bolt is to be mounted, does not restrain the seat surface 73 from being pressed against the portion where the bolt is to be mounted, and forms the annular liquid-tight sealing portion for the portion where the bolt is to be mounted. The bolt of WO2008/10523 invention is especially effective for preventing the occurrence of electrolytic corrosion.
The bolt disclosed in the patent document 1 has an effect to some extent, but is demanded to have higher liquid-tight sealing performance. The bolt disclosed in the patent document 2 has sufficient sealing performance, but the unconductive resinous ring-shaped member projects beyond the bolt body. Thus the entire head part is large and portions where the bolt can be used are limited to specific portions.
Therefore it is an object of the present invention to provide a male fastening tool which is not large and is capable of imparting sufficient liquid-tight sealing performance to a portion to which a member is to be fastened.